Activity in both hippocampus and perirhinal cortex predicts the memory strength of subsequently remembered information

Abstract

It has been suggested that hippocampal activity predicts subsequent recognition success when recognition decisions are based disproportionately on recollection, whereas perirhinal activity predicts recognition success when decisions are based primarily on familiarity. Another perspective is that both hippocampal and perirhinal activity are predictive of overall memory strength. We tested the relationship between brain activity during learning and subsequent memory strength. Activity in a number of cortical regions (including regions within the "default network") was negatively correlated with subsequent memory strength, suggesting that this activity reflects inattention or mind wandering (and, consequently, poor memory). In contrast, activity in both hippocampus and perirhinal cortex positively correlated with the subsequent memory strength of remembered items. This finding suggests that both structures cooperate during learning to determine the memory strength of what is being learned.

Figure 1

Recognition memory task. In the scanner, participants rated (pleasant/unpleasant) 360 words (2.5 s/word). Words were intermixed with 864 1.25-s baseline trials in which participants indicated whether a digit was odd or even. At test (about 15 min later, out of the scanner), participants made confidence ratings (1–6, 1 = “definitely new”, 6 = “definitely old”) for the 360 studied words and 360 novel words (3.5 s/word).

Figure 2

Behavioral performance. Proportion of targets (black bars) and foils (white bars) endorsed at each confidence level (1 = “definitely new” and 6 = “definitely old”). Error bars indicate SEM.

Figure 3

Regions where activity correlated negatively with subsequent memory strength. A linear trend in fMRI activation that predicted subsequent memory strength was observed in (A) right anterior prefrontal cortex (R ant. PFC), (B) right posterior prefrontal cortex (R post. PFC), (C) bilateral inferior parietal cortex (L inf. Par. and R inf. Par.), and medial parietal cortex (midline). Regions of activation are shown superimposed on the averaged T1-weighted scans of all 14 participants. (D) Activation in each of the five regions as a function of the subsequent strength of recognition memory. Error bars indicate SEM.

Figure 4

fMRI activation in the medial temporal lobe as a function of subsequent memory strength. Activation in (A) left temporopolar cortex (L TPC), (B) left perirhinal cortex (L PRC), right hippocampus (R H), and (C) left hippocampus (L H) varied as a function of the subsequent strength of remembered items (4, 5, or 6). Regions of activation are shown superimposed on the averaged T1-weighted scans of all 14 participants. (D) Activation in each of the four regions as a function of the subsequent strength of remembered items. Error bars indicate SEM.